For drugs that are excreted primarily by the kidneys, extreme care is needed with respect to the dose of drug and its dosing interval in the case of kidney damage or renal impairment. The following equations will be more useful for drug dose adjustment in renal failure:

From above equation it can be write that,

If the Cave as a normal individual is desired in a patient with renal impairment, then the following equality should hold:

In the above equation, “n” & “ri” indicate normal and renally impaired conditions respectively. This equation is very useful for calculating dose and dosing interval in individual with renal impairment.

**Related:** Creatinine Clearance Calculation Formula

**Example - 1:**

Thus, the above example shows that the dose has to be reduced from o.27 mg to 0.216 mg in order to maintain the same plasma concentration in renally impaired patient compare in respect to a normal patient.

**Related: **Dosage Calculation Based on Age

**Example - 2:**

**Read also:** Rate of Flow Calculation in Pharmacy

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